Non-imaging illumination incidence angle detection system

Abstract

A non-imaging detector for directly measuring the angle of incidence of irradiation in one plane from an illuminating source. The detector includes a slit mask that transmits narrow lines of irradiation across an array of detectors closely underlying the slit mask. The detectors are configured to generate photocurrents whose ratio exponentially increase as the irradiation lines through the slits move along the array in response to changes in angle of incidence. The detectors are configured according to an exponential formula so that adjacent rows of detectors produce photocurrents so that the photocurrent log difference from adjacent rows will result in a signal directly proportional to incidence angle when subtracted by associated circuitry.

What is claimed is: 
     
       1. A detector for determining the angle of incidence of an illuminating source in a plane normal to said detector, said detector including: an opaque planar slit mask having at least one narrow transparent straight slit in the opaque plane of said mask;   a detector array in a plane parallel with and spaced from said planar slit mask, said detector array including: a plurality of adjacent identical detector elements, the longitudinal axis of each of said plurality of elements being parallel with each other and perpendicular to said transparent slit;   the surface of each of said plurality of elements adjacent said slit mask being configured to produce a maximum detector photocurrent from irradiation through said slit falling across the first end of said element surface and a minimum detector photocurrent from irradiation through said slit falling across the second end of said element surface;   the pattern configuration on the surface of each of said plurality of detector elements being reversed from that on the surface of adjacent elements whereby said first end of one of said elements lies adjacent the second end of an adjacent one of said elements;     first conductive means coupled to the first surface of said plurality of detector elements in said array;   second conductive means coupled to the second surface of alternate ones of said plurality of adjacent detector elements; and   log means associated with said detector elements for generating first and second log signals corresponding to photocurrents generated by said adjacent elements.   
     
     
       2. The detector claimed in claim 1 wherein said detector array includes a plurality of adjacent strips, each strip forming a plurality of detector elements, the plurality of elements in each of said strips being connected in series with one of said second conductive means, the pattern configuration of detector elements in each of said plurality of strips being reversed from the pattern configuration of elements in adjacent strips. 
     
     
       3. The detector claimed in claim 2 wherein the pattern configuration of each of said detector elements includes said log means and wherein the longitudinal movement of a thin transverse light beam along said element will generate, through said first and second conductive means, photocurrents having an exponential amplitude ratio. 
     
     
       4. The detector claimed in claim 2 wherein each of said strips of detector elements is formed of a detector material having an attached overlying opaque mask having a pattern revealing each of said plurality of detector elements and said second conductive means lying along the top longitudinal center of each of said plurality of elements. 
     
     
       5. The detector claimed in claim 4 wherein each of said plurality of elements revealed by said overlying mask includes first and second interconnected detector sections each occupying half the length of each element, said first section having a constant width throughout its length, said second section having a width at its first end that corresponds with that of said interconnected first section and being reduced therefrom to the second end of said section according to an exponential curve. 
     
     
       6. The detector claimed in claim 5 wherein the second section of each of said plurality of detector elements is reduced from the first end to the second end of said section in a curve following the equation: ##EQU3## wherein n1=Index of Refraction of said overlying mask n2=Index of Refraction of air   X=Longitudinal position from first end of said second section   H=Spacing between the surface of said detector element and said opaque planar slit mask,   K=a scale factor.   
     
     
       7. The detector claimed in claims 2, 3 5, or 6 further including first and second electrical conductors, said first conductor coupled to said conductive means in alternate strips of said detector element, said second conductor coupled to the remaining strips of detector elements, said detector further including first and second logarithmic circuits respectively coupled to said first and second conductors for generating first and second output signals proportional to the natural log of the photocurrents in said first and second conductors, respectively, and difference circuitry coupled to said first and second logarithmic circuits for subtracting said first and second output signals to produce an output signal directly proportional to the angle of incidence of irradiation in a plane normal to said detector.